Method for utilizing distillation fractions obtained from distillation of tall oil in btl or cellulose factory

ABSTRACT

The invention relates to a method for utilizing distillation fractions obtained from distillation of tall oil in a BtL plant. The essential feature of the method allows utilization of tall oil obtained from cellulose plants that is processed into different fractions and passed to different points of the BtL process for producing biofuels and utilizing the same in the gasification step and/or energy generation for the BtL process.

The invention relates to a method in accordance with the preamble ofclaim 1 for utilizing distillation fractions obtained from distillationof tall oil in a BtL or, when necessary, in a cellulose factory. Theinvention also relates to a use in accordance with claim 8.

In the art of biomass gasification are known low-temperature andhigh-temperature techniques that respectively operate either below orabove the melting point of ash. Low-temperature gasifiers typicallyoperate at a temperature of 1000° C. maximum and are implemented aseither fixed-bed reactors (power rating less than 20 MW) or asfluidized-bed reactors (power rating above 20 MW). Fuel is fed intothese reactors generally as a mass of solid, comminuted particles.Respectively, gasification takes place either above a fixed-beddistributor or in a fluidized bed. Use of liquid or gaseous rawmaterials in these gasifier types is difficult.

High-temperature gasifiers are operated at a temperature of about 1400°C. and carry out processes often requiring fuel comminuted to a fineparticle size for firing a burner that serves as the gasifier unit. Thiskind of embodiment is characterized by allowing the burner to berelatively easily fired also with liquid and gaseous raw materials whosecombustion in low-temperature gasifiers is complicated. Typicallyhigh-temperature gasifiers are operated as pressurized reactions usingoxygen or a mixture of oxygen and steam and/or carbon dioxide as thegasification agent. A high-temperature gasifier is the gasificationtechnology typically chosen for producing maximally pure syngas, e.g.,for the needs of chemical or oil-refining industries.

In the art is also well known the Fischer-Tropsch method, abbreviated asthe FT method, which is based on a catalyzed chemical reaction whereinsynthesis gas containing only carbon monoxide and hydrogen is convertedinto various paraffinic hydrocarbons that at room temperature generallyare waxy compounds. Typically, iron and cobalt catalysts are used. Theprincipal target of the method is to produce synthetic oil compounds foruse as synthetic fuel or lubricant.

The processing of syngas obtained after cleaning the product gas ofbiomass gasification in an FT reactor and postprocessing of FT productsas an entity is called a Biomass-to-Liquids process, abbreviated as aBtL process.

A Fisher-Tropsch reactor typically gives two end products: a heavier FTwax often denoted as Heavy Fischer-Tropsch Liquid (HFTL) withhydrocarbon chains of about 15 to 100 carbon atoms, and lighter liquidproduct called Light Fischer-Tropsch Liquid (LFTL) with hydrocarbonchains of 5 to 30 carbon atoms. The FT products are taken to a refiningunit designed to be compatible with the FT technique and catalyst usedin the reactor.

The refining unit comprises plural different unit processes. The termhydrogenation unit, also known as a hydrotreater, primarily refers to areactor wherein hydrogen is added to the reactive (unsaturated) bonds ofa molecule. In other words, when a hydrogenated bond becomes saturatedthereby losing its reactivity, the process is called hydrogenation orhydrogen bonding. The term cracking simply means the conversion of largehydrocarbon molecules into a smaller size, whereby this process unit isalso known a hydrocracker (hydrogen addition cracking unit).Isomerization refers to a process wherein hydrocarbon chains arebranched to obtain better fuel qualities for use in engines (i.a.,modification of fuel cloud point). In the final distillation step, thedifferent fuel fractions are separated from each other to obtain endproduct fractions such as diesel fuel, kerosene and naphtha.

Studies have been carried out to improve a BtL plant and itsprofitability. It has been found that a BtL plant may be particularlyadvantageously designed to utilize the byproducts of forest industryplants such as those of the pulp/paper plants. Especially the use ofbyproducts obtained from a sulfate cellulose plant in a BtL plant maybring up mutual benefits.

Among the byproducts of a sulfate cellulose factory one is crude talloil by an average amount of 35 kg per ton of cellulose. The tall oilcomposition varies by wood species, growth location and annual season offelling, whereby it contains about 35-70% fatty acids, 20-50% resinacids, while the remaining portion consists of 5-30% of neutralcomponents. Today, a very minor amount of crude tall oil is used inunprocessed form. The major portion of crude tall oil is distilled intoproducts that are consumed in, e.g., paint and adhesive manufacturingplants and production of tall oil soap. It must be noted that tall oilas a fuel is very close to fuel oil with a heat value of about 38 MJ/kg,which is greater than 90% of the heat value of fuel oil. Moreover, as alow-ash/low-sulfur fuel, tall oil is readily combustible or gasifiablein a modified oil burner.

Concurrently, cellulose plants generally sell tall oil due to its veryhigh energy content for use as an industrial raw material outside theirown processes. While the use of tall oil as a raw material for biofuelhas been investigated, implementing such a refinery unit in conjunctionwith cellulose plants would make it too small in size and, hence, anunprofitable investment. Besides the need for pressurized processing,one additional limitation is the need for pure hydrogen that elevatesthe operating costs of the process excessively. A further problem isthat heavy-fuel-oil-like character of tall oil requires its storagetemperature to be kept in excess of 60° C., whereby its shipping alsodictates special actions such as transport in insulated containers.

Still another hindrance arises therefrom that crude tall oil is notdirectly suitable as feedstock in an oil refinery unit, because theheavy hydrocarbon chains of the oil require special treatment proceduresthus prohibiting its direct mixing with a synthetic biofuel. Moreover,the sulfur content of crude tall oil is high enough to prevent catalyticpostprocessing.

However, tall oil can be used as feedstock for a gasifier with theprovision that the gasifier has a burner-type gasifier unit.Unfortunately, this alternative bypasses the already recognized highrefining potential of tall oil and exploits only the energy content ofthis byproduct. Additionally such an infeed to a low-temperaturegasifier is difficult to arrange as these gasifiers generally arefixed-bed or fluidized-bed reactors.

Now the present invention offers an arrangement capable of utilizing allthe potential of tall oil. An essential benefit results therefrom that aprocess according to the invention can also receive tall oil from pluralcellulose plants. In a preferred embodiment of the invention, adistillation column is erected for processing tall oil. Herein,distillation means separation of the feedstock components from eachother by evaporation. As the separate components condense at differenttemperature ranges, they can be recovered in the distillation process asseparate fractions, i.e., separate distillates, so that one fraction maycontain one or more components. In this fashion the light fractions arerecovered as a distillate whose hydrocarbon chains are closely similarto the HFTL liquid generated in an FT reactor thereby principallycomprising different kinds of fatty acids. These fractions are processedin a single hydrocracker, whereby the product yield of high-quality,high-biofuel-status end products in the BtL plant is elevatedsubstantially. The refining process becomes economically viable inasmuchas the BtL plant already runs a correct process that can be utilized inthe refinement of the tall oil distillate. In the arrangement accordingto the invention only the size and catalyst composition of reactors needbe modified if necessary.

Complementing the first step, the heavy and low-quality fractions notdirectly usable as vehicle fuel obtained from the distillation processare gasified in the gasification process of the BtL plant whereby thisprocess most advantageously is a high-temperature pressurized oxygengasifier. These fractions typically are comprised of resin acids. As theamount of hydrocarbons is thus increased, more syngas can be processedthat in turn improves the product yield of FT products and the overallproductivity of the entire plant. In a similar fashion, the light,gaseous fractions of the distillation process are combined with theother gaseous process products of the BtL plant, whereby they areutilized as a hydrogen or energy source in the BtL plant processes orboilers of a power plant.

An essential feature of the arrangement according to the invention is toutilize tall oil in a BtL plant, most advantageously in a BtL plantdirectly integrated with a cellulose plant. The essential features ofthe invention are crucial to the disclosed method and its use asspecified in the appended claims. More specifically, the invention ischaracterized by what is stated in the claims. The essential goal of theinvention is to utilize tall oil in the process steps of a BtL plant insuch a fashion that the end product is a high-quality biofuel.

In the following, the invention is described in more detail with thehelp of a preferred embodiment by making reference to appended FIGS.1-3, in which drawings:

FIGS. 1-3 show some process diagrams of arrangements for implementingthe method according to the invention.

The process described below is related to a method depicted in FIGS. 1-3for utilizing tall oil in a BtL plant. An essential feature of theinvention is that a BtL plant using the method can utilize tall oil inits different processes. An advantageous alternative is to run theprocess integrated in particular with a sulfate cellulose plant in sucha fashion that the BtL plant uses crude tall oil obtained from thesulfate cellulose plant, whereby the crude tall oil is passed along apipeline to a distillation column integrated with the refinery unit ofthe BtL plant.

FIG. 1 illustrates the stages of a BtL process. Solid biomass 19 isfirst taken to a biomass preprocessing step 1, wherein the biomassparticle size and moisture content are homogenized. Next, thepreprocessed biomass is fed to a high-temperature gasification step 2,whereto oxygen is passed from an oxygen plant 3. The gasification stepmay comprise a pregasification step, wherein the biomass is coked ortorrefied, whereupon the pyrolysis gases released by the biomass aretaken to a high-temperature oxygen gasifier and resulting product ismilled and either passed to the burners of the high-temperature oxygengasifier or the coke can be subjected to so-called chemical gasquenching, whereby the hydrogen content of the syngas increases and, dueto endothermic reactions, the syngas is cooled. The water required inthe reaction comes to the process along with the biomass or water may beinjected separately into the gasifier.

C+H₂O->CO+H₂

CO+H₂O->CO₂+H₂

The gas generated in the gasifier is cooled in a heat exchanger 4 andcleaned free from solid impurities in step 5. Next, the syngas pressureis elevated to the operating pressure of the refinery unit with the helpof a compressor 6. The syngas hydrogen-carbon monoxide ratio is adjustedin step 7 and other components except for hydrogen and carbon monoxideare removed from the syngas in steps 8, whereupon the syngas can be fedto a Fischer-Tropsch reactor 9. The FT fractions exiting the FT reactorare refined in the refinery unit 10 of the plant and thereupon distilledin distillation column 11 into end products 13.

As shown in FIG. 1, in the preprocessing step 12 of tall oil 18, fromtall oil 18 are separated those hydrocarbon fractions 14 a/14 b that dueto their distillation properties and other qualities are close to theHFTL fraction processed in the FT reactor 9 from the syngas 8. Thenonliquified light hydrocarbon fraction 17 are separated and used inenergy generation, for instance.

Depending on the tall oil preprocessing procedures and operatingparameters of the refinery unit, the fatty oil distillates can be fedeither via unit 14 a to the hydrocracking process of the refinery unitor via unit 14 b to end-product distillation. The difference betweenthese alternatives is illustrated in FIGS. 2 and 3.

When necessary, the refinery unit 10 of the BtL plant can be designedfor an oversize capacity, whereby it can also process tall oil 18received from plural sources. If a need in the process arises thereto,the hydrocracker unit can be complemented with a sulfur-removal facilityor other modifications. No new process equipment or other postprocessingsteps are required as will be described later in the text. In thisfashion according to the invention, the light fractions of crude talloil are processed into hydrocarbon chains of desired length and qualitythat are suited for processing high-quality biofuels.

The heaviest tall oil fractions generally known as bottoms distillate,bottoms oil or bottoms fraction 15 are processed in the gasificationreactor 2 of the BtL plant and/or are used in energy generation 16.Furthermore, if necessary, the bottoms fraction 15 may be returned tothe cellulose plant and burnt there in a lime kiln. According to theinvention, the bottoms fraction (bottoms distillate) 15 of thedistillation column contains tar-like hydrocarbon compounds of longcarbon chains (longer than C₃₀) that are kept in a fluid state and nextpumped from a storage container to the gasification reactor 2 of the BtLplant. The gasification reactor 2 is a pressurized oxygen gasifier mostadvantageously operated at a high temperature, whereto the comminutedbiomass is fed in pulverized form into the burner section of thereactor, wherein it reacts with oxygen to produce raw syngas. Thehigh-temperature gasifier facilitates a very simple arrangement for thegasification of the tall oil bottoms fraction. The gasifier needs aninfeed distributor whereon the heated bottoms fraction is pumped. Thefeedstock will gasify completely and its ash will mix with the ash ofthe other raw material being combusted. No other new process equipmentor refining steps are required as described later in the text. Anessential feature is that depending on the amount of tall oil feedstock,the capacity of a BtL plant may be increased by as much as 5-50% withregard to a plant not using tall oil as feedstock.

In FIG. 2 is illustrated an embodiment of a distillation process in moredetail. Therein, tall oil 18 is fed into a distillation column 12. Fromthe bottom of distillation column is removed tall oil in liquid form andpassed to a heater 20, wherein the tall oil is evaporated. By virtue ofkeeping the heater temperature at a given level, the light fatty acidsevaporating at a lower temperature are vaporized while the heavierfractions respectively remain in liquid form. Suitable temperature forthe heater is 150-350° C. Heating of the tall oil can be performed usingvarious heat sources 31 available in a BtL plant such as steam,combustible gases or a portion of bottoms fraction 15 separated in theprocess.

Steam released from the distillation column 12 is condensed with thehelp of cooling water in a condenser 21 and the condensate is taken to aclarifier 22. Noncondensing gases 17 are passed from the condenser 22 toenergy generation. Waste water 23 evaporated in the distillation columnand condensed in the condenser is removed from the process. The lightfraction 14 of tall oil principally comprising fatty acids are taken viaa buffer container 24 to postprocessing. This variant of the inventionis shown in FIG. 1 as alternative 14 a, wherein if necessary a portionof the fraction is returned to the top of distillation column 12 toimprove the temperature profile of the column.

In FIG. 3 is shown another embodiment, also illustrated as alternative14 b in FIG. 1, wherein tall oil is processed further prior to feedingthe distilled fractions to the BtL process. The embodiment of FIG. 2 isbased on the assumption that the catalyst used in the hydrocracking ofBtL products is also suitable for processing tall oil distillates.However, this is a challenging demand with respect to the catalyst beingused inasmuch as tall oil contains sulfur that acts as a catalystpoison. Furthermore, it is most undesirable to allow sulfur to pass tothe end product. In the embodiment shown in FIG. 3, the hydrocrackingcatalysts can be chosen separately for tall oil and biowax.

As shown in FIG. 3, tall oil 18 is passed to distillation column 12 viaa possible pretreatment step 26. Herein, the pretreatment step 26 means,e.g., esterification of the fatty/resin acids of tall oil with the helpof an additive 25, in the present case most advantageously withmethanol. Sulfur 30 is removed from the fraction separated indistillation column 12, because it acts as a catalyst poison in thepostprocessing unit 27. After the hydrogenation step 28, the distillateis condensed in step 21 and clarified in step 22.

In FIG. 3 is depicted as a horizontal dashed line the balance line ofprocess flows between the BtL plant 32 and tall oil processing unit 33so that the BtL plant 32 is to the left and tall oil processing unit 33is to the right.

In the process according to the invention shown in FIG. 3, significantbenefit is attained by complementing a BtL plant 32 with a tall oilprocessing unit 33. In this arrangement, hydrogen sulfide 30 fromdesulfurization can be treated in conjunction withhydrogen-sulfide-containing gas separated in the acid gas scrubber ofthe BtL process in the same catalytic or thermal gas treatment equipmentto reduce its harmful release to the atmosphere. The BtL plant 32provides hydrogen 29 stemming from the processing of the biomass,whereby biofuel status of process stays high. The BtL plant 32 includescooling-water and waste-water processing facilities 23. Combustiblegases 17 can be utilized either in the refinery unit furnaces of the BtLplant or, alternatively, the sulfur-free process gases can be reformedto produce hydrogen. The hydrogenated distillate 24 can be fed as asidestream to the final distillation of the BtL product, while thebottoms distillate 15 is used in gasification or energy generation. Ifthe tall oil-based biofuel is desired to be kept apart from the BtLbiofuel, the distillate 24 may be later distilled into end products in aseparate distillation plant. Furthermore, the BtL plant 32 providesenergy in the form of steam or gases for heating the distillationequipment 31.

In accordance with the above, it is obvious that the invention providessignificant benefits via the essential feature of the invention allowingthe use of tall oil as feedstock in a BtL plant in the production abiofuel and facilitating efficient use of bottoms distillate ingasification, black liquor combustion or energy generation.

To a person skilled in the art it is obvious that the invention is notlimited by the above-described exemplary embodiments, but rather may bevaried within the inventive spirit and scope of the appended claims.

1. A method for utilizing distillation fractions obtained fromdistillation (18) of tall oil (18) in a BtL plant (32), characterized inthat the method utilizes tall oil (18) obtained from cellulose plantsand processed into different fractions and passed to different points ofthe BtL process for producing biofuels and utilizing the same in thegasification step (2) and/or energy generation (16) of the BtL process.2. The method of claim 1, characterized in that in the method to therefinery unit of the BtL plant (32) is integrated a fractionatingdistillation column (12), wherein the tall oil (18) is separatedsubstantially into two fractionated streams of tall oil such that thelighter fraction (14 a/14 b) is processed further into hydrocarbonchains suited for producing high-quality biofuels while the heavierbottoms fraction (15) is passed to the gasification process (2) and/orenergy generation (16) of the BtL plant.
 3. The method of claim 1,characterized in that in the method the tall oil distillate (14 a/14 b)separated in the fractionating distillation column (12) is passed to aclarifier (22), wherein is separated the fraction that is to be refinedand has a composition similar to the HFTL fraction produced in an FTreactor, while the remainder (17) of the lighter fractions is utilizedin energy or hydrogen generation, for instance.
 4. The method of claim3, characterized in that in the method the lighter fractions (14 b) ofthe tall oil distillate having a composition similar to the HFTLfraction produced in an FT reactor are pretreated (26) prior toseparation in the fractionating distillation column (12), whereuponafter the separation step the lighter fractions (14 b) are passed to arefinery unit (27) and therefrom further to a hydrocracker (28).
 5. Themethod of claim 1, characterized in that in the method the heavier talloil bottoms fraction (15) received from the distillation column (12) ispumped to the gasification reactor of the BtL plant (32), advantageouslya high-temperature gasification reactor (2) and/or, when necessary, isused in energy generation (16) or is returned for combustion in the limekiln of the cellulose plant.
 6. The method of claim 5, characterized inthat in the method the high-temperature gasification reactor (2) is apressurized oxygen gasifier whereto is fed the tall oil bottoms fraction(15) that joins with the gas resulting from the treatment of biomass inthe reactor burner and reacts with oxygen thus generating raw syngas. 7.The method of claim 1, characterized in that depending on the amount oftall oil feedstock, the product yield of the BtL plant (32) increases by5-50%.
 8. Use of tall oil (18) as feedstock in a BtL plant (32) forproduction of a synthetic biofuel and utilization thereof in thegasification step (2) of the BtL process and/or in energy generation(16).
 9. The use according to claim 8 such that the BtL plant (32) isadvantageously integrated with a cellulose plant, whereby the BtL plantutilizes tall oil (18) obtained from the plant integrated therewith and,when necessary, from other cellulose plants for producing biofuel andutilizing the same in the gasification step (2) of the BtL processand/or in energy generation (16).
 10. The use according to claim 8 oftall oil (18) so that the tall oil is separated prior to thegasification step (2) of the BtL plant (32) in a fractionatingdistillation column (12) into a light tall oil fraction (14 a/14 b) thatis processed together with HFTL fraction obtained from the BtL process.11. The use according to claim 8 of tall oil (18) so that the tall oilis preprocessed (26), refined (27) and passed to a hydrocracker (28)thereby producing a tall oil fraction (14 b) that is passed forward as asidestream to the final distillation step of the BtL product forproducing a biofuel.
 12. The use according to claim 8 of tall oil (18)so that the heavier bottoms fraction (15) obtained from the distillationcolumn (12) is utilized in the gasification process (2) and/or energygeneration (16) of the BtL plant or in the lime kiln of the celluloseplant whereto the BtL plant is integrated.
 13. The method of claim 2,characterized in that in the method the tall oil distillate (14 a/14 b)separated in the fractionating distillation column (12) is passed to aclarifier (22), wherein is separated the fraction that is to be refinedand has a composition similar to the HFTL fraction produced in an FTreactor, while the remainder (17) of the lighter fractions is utilizedin energy or hydrogen generation, for instance.
 14. The method of claim2, characterized in that in the method the heavier tall oil bottomsfraction (15) received from the distillation column (12) is pumped tothe gasification reactor of the BtL plant (32), advantageously ahigh-temperature gasification reactor (2) and/or, when necessary, isused in energy generation (16) or is returned for combustion in the limekiln of the cellulose plant.
 15. The method of claim 2, characterized inthat depending on the amount of tall oil feedstock, the product yield ofthe BtL plant (32) increases by 5-50%.
 16. The method of claim 3,characterized in that depending on the amount of tall oil feedstock, theproduct yield of the BtL plant (32) increases by 5-50%.
 17. The methodof claim 4, characterized in that depending on the amount of tall oilfeedstock, the product yield of the BtL plant (32) increases by 5-50%.18. The method of claim 5, characterized in that depending on the amountof tall oil feedstock, the product yield of the BtL plant (32) increasesby 5-50%.
 19. The method of claim 6, characterized in that depending onthe amount of tall oil feedstock, the product yield of the BtL plant(32) increases by 5-50%.
 20. The use according to claim 9 of tall oil(18) so that the tall oil is separated prior to the gasification step(2) of the BtL plant (32) in a fractionating distillation column (12)into a light tall oil fraction (14 a/14 b) that is processed togetherwith HFTL fraction obtained from the BtL process.